Because he SOUNDS very defiant. Obviously, no one likes being pushed around, and he seems to feel pressured to do something he apparently is not prepared to do. Which on one level is just sad to witness. We've all watched people we love get older and get to the point of real failing health. But it's also frustrating to feel like, despite acknowledging he somewhat did this to himself with his disastrous debate performance, he's still not accepting the legitimacy of the worry about his capabilities. My hope is honestly that the least bad of the two bad options is true, which is that Biden was, like so many before him, enticed by the power of the Oval Office and found himself unwilling to let it go once he was the incumbent. Because the other option is he's lost his marbles almost completely and is being led by the people around him.
I also am not sure what is going on with Congress - I suspect that they, like voters who were thrown by Biden's debate performance, feel misled. I think Biden's team has been doing a lot to hide his failing health, and from the reaction of several Congress members, that wasn't just happening in front of the camera, it was happening behind the camera too. Probably the ones who are the loudest are the ones who had private misgivings and his team made an effort to assure them, and now they feel like they were lied to. I'm seeing somewhat of an attempt to turn it around in the last two days, refocus on things like Project 2025, but I think initially, they were taken aback, very angry, and very scared to find themselves in a different position than they thought they were in. It's also possible some of them were very aware of Biden's health issues but believed he could mask it better until the debate.
Really, we as voters have some culpability here too. We find ourselves here again and again and again - Reagan, McCain, Feinstein, now Chuck Grassley. This truly is a "both parties" failure, heh. And Trump himself is part of the same problem. It can be hard to focus on because of everything else that's so terrible about him, but Trump is not really doing any better cognitively speaking than Biden and he may well be worse. We seem to just not want to have a difficult reckoning that it gets to the point where it's no longer a good idea to vote back in the incumbent. I'm not sure what the solution is, because age limits can be arbitrary to some extent - Pelosi still seems sharp as a tack, for example. But it's a problem we're not dealing with and it's led us here, where we desperately needed to be at the absolute top of our game to combat Trump and Project 2025, and instead we have a President and candidate in obvious declining health.